Markdown Linter
Find common Markdown style and consistency issues — trailing whitespace, hard tabs, extra blank lines, heading spacing, inconsistent list markers — and auto-fix them. Runs in your browser; nothing is uploaded.
About this tool
Markdown Linter checks your Markdown for common style and consistency problems and can auto-fix them. Paste a document, pick a mode, and either get a clear list of issues or a cleaned-up version back.
Mode
- check — report every issue found, one per line, as
line:col rule message(with a summary count and how many are auto-fixable). - fix — return the corrected Markdown with all fixable issues applied. Any issue that needs a human decision is listed in a trailing HTML comment.
What it checks
- MD001 — Heading levels increment by one (catches a skipped level like H1 → H3).
- MD009 — Trailing whitespace (a deliberate two-space hard line break is kept).
- MD010 — Hard tabs (expanded to spaces on fix).
- MD012 — Multiple consecutive blank lines (collapsed to one).
- MD018 — No space after
#on a heading (#Heading→# Heading). - MD019 — Multiple spaces after
#(# Heading→# Heading). - MD022 — Heading not preceded by a blank line (a blank line is inserted).
- MD025 — Multiple top-level H1 headings (flagged for review).
- MD026 — Trailing punctuation in a heading (the
./,/;/:/!is removed). - MD004 — Inconsistent unordered list markers (
*,+,-normalized to the first one used). - MD040 — Fenced code block missing a language (flagged for review).
- MD047 — Missing final newline (added; trailing blank lines removed).
Fenced code blocks (``` and ~~~) are respected, so prose rules like heading
spacing and trailing punctuation never fire on code — but whitespace rules (tabs,
trailing spaces) still apply inside them.
Everything runs locally in your browser via WebAssembly — your Markdown is never uploaded.
Handy for
- Cleaning up README and docs before committing.
- Enforcing a consistent house style across a docs folder.
- Quickly spotting why a Markdown renderer is misbehaving (stray tabs, bad heading spacing, mixed list markers).
FAQ
Why does fix mode leave some issues unfixed?
Three rules need a human decision: a skipped heading level (MD001), multiple H1s (MD025) and a code fence with no language (MD040) can each be "fixed" in more than one valid way. Fix mode applies everything mechanical and lists these remaining items in an HTML comment at the end of the output, so the document still renders cleanly.
Will the linter strip my two-space hard line breaks?
No. MD009 flags trailing whitespace, but a line ending in exactly two spaces is the standard Markdown hard line break and is deliberately kept — only other trailing spaces (one, or three-plus) are reported and removed.
Does it lint inside code blocks?
Partially, on purpose. Prose rules (heading spacing, trailing punctuation,
list markers) never fire inside ``` / ~~~ fences — a # comment in a shell
snippet is not a heading. Whitespace rules (hard tabs MD010, trailing spaces
MD009) still apply there, since they bite in code too.
Is this the same rule set as markdownlint?
It implements a 12-rule subset of the widely used markdownlint (MD0xx) rules — the high-signal ones listed above — with the same rule IDs, so findings map directly onto markdownlint documentation. There's no config file; the rules run with their common defaults.
Developer & Automation Access
Run it from the terminal
Same engine as this page, headless — via the gizza CLI:
gizza tool markdown-lint "# My doc
Paste your Markdown here."New to the CLI? Get gizza →
Open it by URL
Pre-fill and auto-run this tool with query parameters — the names match the API/CLI:
https://gizza.ai/tools/markdown-lint/?markdown=%23%20My%20doc%0A%0APaste%20your%20Markdown%20here.&mode=checkMachine-readable descriptor: tool.json — title + parameters JSON Schema for agents.